Sep 25, 2013 6:59 PM

This rock measures approx 4.5cm x 3 cm. It is shiny and filled with black flecks. It was found in the Matusadona national park in the Lower Zambezi valley in the north of Zimbabwe. There were no other rocks similar to this in the area it was found.

This brief description of the area talks of sedimentary rocks one side of the Zambezi escarpment and metamorphics (gneisses) the other. Your specimen is neither of those.

It is an igneous rock, but it is difficult to say much useful about it just from a photo of a hand specimen. The dark mineral may be hornblende (I don't think it is biotite, but it might just be a pyroxene), the pale mineral may be feldspar (quite possibly with quartz); just guesses with a smidge of insight from the shapes of the mafics. It is perhaps somewhat unusual to have coarse grained mafic (dark) minerals in a fine-grained pale matrix. Because of the fine-grained pale matrix it could be termed a felsite, and that can be qualified by the mafic phenocrysts - so it might be a hornblende felsite. It might also be possible the describe it as a coarse lamprophyre.

Given microscopic analysis, one could say for certain of what minerals and textures it was composed, and hence give a name to the rock type.

Good find - very interesting, although not coprolites you have found something very different.

They are not at all common but I have attached a few images of coprolites from the Yorkshire coast.

The first two are probably only found in this type of preservation called a pyritic nodule (aka Cannonball) they possibly come from an Ichthyosaur, Plesiosaur,Shark or other type of Lower Jurassic fish.

I will post some more recognisable images of coprolites from my collection soon.